Tisin coating method

ABSTRACT

A method for ALD coating of a substrate with a layer containing Ti, Si, N, wherein a reaction gas and then a flushing gas are introduced into a process chamber holding the substrate in a plurality of successive steps, each in one or more cycles, wherein TiN is deposited in a first step with a reaction gas containing Ti and a reaction gas containing N, TiSi is deposited in a second step with a reaction gas containing Ti and a reaction gas containing Si, and in a third step following the second step, TiSiN is deposited with a reaction gas containing Ti, with a reaction gas containing N and with a reaction gas containing Si.

INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/612,853 entitled “TiSiN Coating Method,” filed Jun. 2, 2017, thecontent of which is incorporated by reference in its entirety. Any andall applications for which a foreign or domestic priority claim isidentified in the Application Data Sheet as filed with the presentapplication are hereby incorporated by reference under 37 CFR 1.57.

BACKGROUND Field of the Invention

The invention relates to a method for ALD coating of a substrate with alayer containing Ti, Si, N.

Description of the Related Art

In the ALD method, a layer consisting of a plurality of chemicalelements is deposited on a substrate in several successive cycles.Reaction gases containing at least one element that is to be depositedin the layer are used in this process. In these cycles, layers of thesame elements or a group of elements are deposited, layer for layer, areaction gas being introduced into the process chamber in each case andremaining there in the process chamber until the surface of thesubstrate has become saturated with the reaction gas. In a subsequentFlush or purge step, the residues of the process gas are removed fromthe process chamber and the same reaction gas or another reaction gas isintroduced into the process chamber. The deposition process takes placeat elevated temperatures at which a chemical reaction takes place on thesubstrate surface; in particular a decomposition reaction of thereaction gas may take place on the substrate surface. Volatile reactionproducts are removed from the process chamber with the flushing gas.

The aforementioned document discloses a method for deposition of adiffusion barrier on a layer sequence of an electronic component, forexample, a memory component made on silicon substrates, wherein thelayer not only serves to limit diffusion but should also be electricallyconductive in order to be used as a contact. In a first step a TiN layeris deposited there and then an SiN layer is deposited. The individualcycles are carried out several times one after the other in such a waythat a TiSiN layer is formed on the whole.

The diffusion resistance of the layer can be increased by increasing thesilicon content. When the silicon content is increased in the knownprocess, the electric resistance of the deposited layer increases at thesame time, so that the properties of the layer are inferior if it shouldact as a contact layer.

US 2015/0279683 and U.S. Pat. No. 6,911,391 also relate to a method fordeposition of TiSiN layers on substrates.

Such a method is described in US 2015/0050806 A1.

SUMMARY

The object of the invention is to provide measures with which adiffusion barrier is increased with regard to its diffusion resistancebut at the same time the electric conductivity is not impaired.

This object is achieved by the invention defined in the claims, whereinthe dependent claims are not just advantageous refinement of the methoddefined in the independent claim but also constitute independentapproaches to solving the problem, wherein individual subfeatures of theindependent claims also have independent inventive significance.

First and essentially, it is proposed that after an obligatory heatingstep following transport of the substrate into the process chamber, TiNis deposited on the substrate and/or on a layer already deposited on thesubstrate, in particular a polysilicon layer. Next an N-free layer orlayer sequence of Ti and Si is deposited. Then a TiSiN layer or layersequence is deposited on the TiS layer. This takes place in threechronologically successive steps, each step being carried out at leastonce, preferably at least one of these steps or all of these steps beingcarried out several times in succession. In the first step, a cycle iscarried out n times for deposition of TiN, first injecting a reactiongas that contains titanium into the process chamber; then flushing theprocess chamber with an inert gas; next containing a reaction gascontaining nitrogen into the process chamber and finally flushing theprocess chamber with an inert gas. Nitrogen or argon or some othersuitable noble gas or any other suitable gas may be used as the inertgas; n may be 1 but is preferably at least 5. The second step mayconsist of two substeps, each of which is carried out at least once; butpreferably is carried out multiple times. In the first substep areaction gas containing titanium is injected into the process chamberand then the process chamber is flushed with an inert gas. The firstsubstep may be carried out m times; where m=1, but preferably is atleast 5. In the second substep a reaction gas containing silicon isfirst injected into the process chamber and then the process chamber isflushed with an inert gas. This second substep may be carried out ktimes; where k=1, but is preferably at least 5. The second step; inwhich a nitrogen-free area of the coating is essentially preferablydeposited; is carried out r times; where r=1, but is preferably at least10. The third step preferably also consists of two substeps, wherein TiNis deposited in a first substep. To do so, essentially the first stepdescribed above is carried out p times. In the first substep of thethird step; a reaction gas containing titanium is first injected intothe process chamber; then the process chamber is flushed with an inertgas. Next a reaction gas containing nitrogen is injected into theprocess chamber and then the process chamber is flushed with an inertgas. This first substep of the third step is carried out p times; wherep=1, but is preferably at least 2. In the first substep of the thirdstep; a reaction gas containing titanium is first injected into theprocess chamber. The process chamber is then flushed with an inert gas.Next; a reaction gas containing nitrogen is injected into the processchamber and then the process chamber is flushed with an inert gas. Inthe first substep of the third step; the coating thus includes an areacontaining nitrogen. A second substep and in particular the lastsubstep, in which only silicon is deposited by injecting a reaction gasthat contains silicon into the process chamber is carried out followingthe first substep, wherein; here again; a cycle consisting of injectingthe reaction gas containing silicon into the process chamber and thenflushing the process chamber with the inert gas is carried out q times,where q=1 or preferably is at least S. The third step, in which TiSiN isdeposited on the whole, can be carried out r times, where r=1 butpreferably is at least 10. It is provided in particular that in carryingout the third step, the reaction gas of the last substep does notcontain any nitrogen. As a result of the method according to theinvention, an area containing TiN, i.e., having Ti—N bonds, is depositedon the layer of the substrate containing silicon in the first step dueto the method according to the invention. A second area, which is a corearea in which essentially Si—Si bonds or Si—Ti bonds are formed, isdeposited on this first area which is a borderline report [sic; area].These bonds have a much lower bond energy (approximately 100 eV) thanthe Ti—N bond in which the bond energy is approximately 450 eV. Thismethod is carried out in particular in such a way that TiSi₂ is formedin different phases and has a lower electrical resistance than TiSiN,for example. To this extent, it is advantageous if an N-free componentis deposited in the last substep of the third step, wherein the reactiongas does not contain any nitrogen component for this purpose which doesnot take part in the chemical reaction although N₂ can. In the last stepa third area of the coating is deposited, this being a borderline regioncontaining nitrogen. The individual layer thicknesses of the threelayers are preferably 2 Å to 200 A with the sum total of the threelayers being 5 A to 500 A. All three layers could be repeated insitu andin sequence to yield film thicknesses of 5 A to 500 A. The gaseouscompounds of titanium, silicon and nitrogen known from the prior art,for example, TiCl₄, TDMAT or TDEAT are used as the reaction gases.Dichlorosilane (SiH2Cl₂) or SiHCl₃, SiCl₄, SiH₄ or Si₂H₆ may be used forthe reaction gas containing silicon. NH₃ or MMH may be used as thereaction gas containing nitrogen. This method begins with heating of thesubstrate to a temperature of 400° C. to 700° C. at a total pressure inthe range between 5 millibar and 0.6 millibar (Equivalent to 0.5 mtorrto 7.5 mTorr). Next the three steps described above are carried out.After cooling the substrate, it is removed from the process chamber. Theterm substrate as used here in particular is understood to refer to aprestructured and precoated wafer on which a structuredsilicon-containing layer sequence has already been deposited, forexample, a layer sequence of a memory module. The TiSiN coatingdeposited according to the invention can then be connected by means ofwires made of copper or the like.

The coating is preferably deposited in a reactor that can be evacuatedusing a vacuum system. Inside the reactor there is a gas inlet elementfor introducing the reaction gases and/or the inert gas. The gas inletelement may be in the form of a shower head. It may have a plurality ofsectors or segments, wherein the segments or sectors form separatechambers into which the reaction gas containing Ti, the reaction gascontaining Si or the reaction gas containing N can be injectedseparately from one another. The gas inlet element may extend over thetotal area extent of the substrate which sits on a heated susceptor. Thegas inlet element may be cooled but it may also be heated. The substrateis preferably sitting on a susceptor which may be heated by a pluralityof heating element so that the susceptor has a plurality of heatingzones which may be heated independently of one another. A uniformtemperature profile can be adjusted on the substrate surface in thisway. In particular, a temperature profile with a minimal lateraltemperature gradient can be adjusted on the substrate surface.

In addition, the invention relates to a coating applied to a substrateand having a first borderline region with which the coating is adjacentto the substrate or to a layer applied to the substrate. The coatingalso has a second borderline region which is opposite the firstborderline region and to which a metallic or metal ceramic contact isapplied. The second borderline region has a surface area, which comes incontact with the contact material. Between the first borderline regionand the second borderline region there is a core region. The inventivecoating has the following properties: the first borderline region has ahigher nitrogen concentration than the core region. The secondborderline region has a higher nitrogen concentration than the coreregion. The core region is preferably free of nitrogen. The surface areaof the second borderline region is preferably free of nitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is explained in greater detail below on the basis ofexemplary embodiments, in which:

FIG. 1 shows the process steps in chronological succession as a blockdiagram,

FIG. 2 shows schematically the structure of a reactor for carrying outthe process in a type of cross section and

FIG. 3 shows the cross section through a gas inlet element of a deviceillustrated in FIG. 2 ,

FIG. 4 shows schematically and on an enlarged scale a layer deposited bythe method according to the invention on a substrate 17.

DETAILED DESCRIPTION

FIG. 2 shows schematically the structure of a coating device arrangedinside a reactor housing 11 that is sealed airtight. A plurality ofinlet lines is provided, such that it is possible to feed a gas streaminto a gas inlet element 12 through each of these feeder lines. The gasinlet element 12 has a plurality of gas outlet openings 13 through whichthe gas fed into the gas inlet element 12 can enter a process chamber10. The bottom of the process chamber 10 is formed by the top side of asusceptor 16 on which the substrate 17 to be coated sits. The susceptor16 can be heated to a process temperature by means of a heater 15.

The susceptor 16 may be rotated about an axis of rotation D in its planeof extent. The rotation takes place relative to the gas inlet element12. A gas outlet 14 to which a vacuum pump is connected is provided.

An inert gas can be fed into a chamber 18 of the gas inlet element 12through a feeder line by means of a first mass flow controller 22. A gascontaining nitrogen can be fed by means of a mass flow controller 23into a chamber 19 separated from the former by an airtight seal. A gascontaining titanium can be fed into a chamber 20 separated from theformer with an airtight seal, by means of a mass flow controller 24. Agas containing silicon can be fed into a chamber 21 of the gas inletelement 12 by means of a mass flow controller 25.

FIG. 3 shows as an example the spatial arrangement of the individualchambers 18, 19, 20, 21 in the gas inlet element 12. The chambers may bearranged like spokes. When the substrate 17 is rotated relative to thegas inlet element 12, the reaction gas or inert gas fed into the processchamber 10 comes in contact with all regions of the surface of thesubstrate 17.

Semiconductor components for memory element or the like haveelectrically active layers containing silicon. These layers must beelectrically contactable in order to connect the layers to bond wires,for example. A TiSiN coating is applied between the contact and thelayer, the process of application of this layer being designed so thatthe layer has the lowest possible electrical resistance while at thesame time forming a high diffusion barrier which prevents the contactmetal applied to the TiSiN coating from diffusing into the siliconlayer. For deposition of this layer, an ALD method (atomic layerdeposition) is used according to the invention. In this method, areaction gas is fed into the process chamber 10 in alternation with aninsert gas for flushing the process chamber 10. This takes place byintroducing the respective gas into the cavity in the gas inlet element12 and discharge the gas from the plurality of gas outlet openings 13arranged like a sieve into the process chamber 10. The reaction gas isfed into the process chamber 10 in such a concentration and over such aperiod of time until the surface of the substrate 17 applied to thesusceptor 16 has become saturated with the reaction gas and/or areaction product of the reaction gas, for example, a decompositionproduct. Then the gas residues are flushed out of the process chamber10. This is accomplished by introducing an inert gas into the processchamber 10, wherein the inert gas may be nitrogen or a noble gas.

According to the invention the coating is applied in a number ofsuccessive coating steps, each of which may in turn comprise substepsand is preferably repeated several times. The process is carried out insuch a way that essentially Si—Si bonds or Si—Ti bonds are formed in thecore area of the coating so that the coating consists mostly of TiSi₂which has a lower electrical resistance than TiSiN. On the other hand,however, the process is carried out in such a way that the interfacefacing underneath layer and the interface of the coating having thesubsequent layer have a higher nitrogen content than the core region ofthe coating. The coating consists essentially of three regions, a lowerinterface connected to the substrate surface and/or the layer containingthe silicon there, said interface consisting essentially of TiN, thecore region of the coating consisting essentially of Ti and Si and anupper interface consisting essentially of TiSiN.

The conduct of the process is explained in greater detail below withreference to the accompanying FIG. 1 . First, in a substrate transportstep (wafer transport) 4, the substrate 17 is introduced into theprocess chamber 10 where the substrate 17 rests on the susceptor 16. Byheating the susceptor 16 with a heater 15 having a plurality of heatingzones, the substrate is heated to a process temperature. This takesplace by passing an electric current through a wire resistor of theheater 15.

In a first process step 1, TiN is deposited. To do so, a reaction gascontaining Ti is first introduced into the process chamber 10 until thesurface of the substrate 17 is saturated with the process gas (Ti). Thenresidues of the reaction gas containing Ti or its reaction productswhich do not remain on the surface of the substrate 17 are flushed outof the process chamber 10 by means of an inert gas (P). Next a reactiongas containing nitrogen is fed into the process chamber until thesurface of the substrate 17 has been saturated with it (N). Next byintroducing the inert gas, the reaction gas containing nitrogen isflushed out of the process chamber 10 (P). These four successivesequences form a first step 1 that is repeater n times resulting in alayer preferably 10 A thick but up to 50 nm thick.

In a second following step 2 the TiSi core material is deposited. Thissecond step 2 consists of two substeps 2.1,2.2, wherein Ti is depositedin the first substep and Si is deposited in the second substep. In thefirst substep 2.1, a reaction gas containing Ti is first introduced intothe process chamber 10 a total of m times and then gas residues areflushed out of the process chamber 10 by introducing an inert gas (P).Following this first substep 2.1 of the second step 2 which is carriedout at least once but preferably several times, the second substep 2.2is performed. In this second substep 2.2, a reaction gas containingsilicon is first fed into the process chamber 10 (Si) and then theprocess chamber 10 is flushed by introducing an inert gas (P). Thesecond substep 2.2 is carried out a total of k times, where k ispreferably greater than 1.

The second step 2 consisting of the two substeps 2.1 and 2.2 ispreferably carried out a total of r times until the required layerthickness of a core layer, which consists of TiSi and is essentiallyfree of nitrogen is deposited, this layer thickness may also bepreferably 10 A thick but up to 50 nm.

The second step 2 is followed by a third step 3 in which TiSiN isdeposited. The third step consists of two substeps 3.1,3.2 which followone another and can be carried out a total of 1 times where 1 is 1 orpreferably greater than 1.

The first substep 3.1 of the third step 3 corresponds essentially to thefirst step 1. TiN is deposited; so a reaction gas containing titanium isfirst fed into the process chamber 10 (Ti)f which is then flushed byintroducing an inert gas (P). Following that a reaction gas containingnitrogen is introduced into the process chamber 10 (N) whereupon theprocess chamber 10 is again flushed by introducing an inert gas (P). Thesubstep 3.1 can be carried out a total of p times where p=1 or ispreferably greater than 1.

The second substep 3.2 of the third step 3 is carried out without theuse of a reaction gas containing N. First the reaction gas containingsilicon is fed into the process chamber 10 (Si). Then the processchamber 10 is flushed by introducing the inert gas (P)f whereupon thesecond substep 3.2 of the third step 3 can be carried out a total of qtimes where q=1 or is preferably greater than 1.

After cooling the process chamber 10, the substrate 17 is removed fromthe process chamber 10 in a transport step (wafer transport) 4.

The gases mentioned in the introduction are used as the reaction gases,for example; the reaction gas containing Ti may be TiCl₄, TDMAT or TDEATand the reaction gas containing Si may be SiH₂Cl₂, SiHCl₃, SiCl₄, SiH₄or Si₂H₆. The reaction gas containing N may be NH₃ or MMH. The inert gasmay be N₂ or a noble gas.

Due to the use of a gas inlet element 12 having chambers 18, 19, 20, 21arranged like sectors around a center; a uniform flow pattern can beachieved within the process chamber. The gas inlet element 12 which isin the form of a shower head can be cooled or heated. A thermalequilibrium can be established. The susceptor 16 may also be heated orcooled. The heater 15 is in particular a multizone heater, preferablytwo heaters being at different distances radially from the center arearranged around the center. The chambers 19 to 21 may each be flushedwith the inert gas in the respective gas change so that no reaction gasremains there.

By means of SiN measurements or XPS measurements, it has been shown thatthe bonding energy between the individual atoms is much lower in thecore region of the layer than in the two interfaces, thus indicatingthat TiSiN is formed only in the boundary regions and essentially Si—Siand/or Si—Ti is formed in the core region.

FIG. 4 shows schematically a section through a coating 30 deposited on asubstrate 17. The substrate 17 is shown only symbolically and includes asilicon wafer with a layer structure deposited on it, wherein theinterface of the substrate 17 facing the coating 30 may be a surface ofa layer containing silicon.

The coating 30 consists of a first boundary region 31, which isdeposited directly on the surface of the substrate 17, a core region 33,which is connected to the first boundary region 31 and a second boundaryregion 32, which has a surface 34 to which a contact wire can beconnected.

The layer 30 deposited with the method described previously has a firstinterface 31, which has an elevated nitrogen concentration, wherein thenitrogen concentration in the first boundary region 31 is greater thanthat in the core region 33. The core region 33 is preferably essentiallyfree of nitrogen. The second boundary region 32 has a higher nitrogenconcentration than the core region 33. The surface 34 is preferably freeof nitrogen.

In the first boundary region 31 and in the second boundary region 32,TiSiN compounds with a high bond energy are formed (TiN 455.6 eV). Inthe core region 33 essentially Si—Si bonds with a bond energy of 99.6 eVand Ti—Si bonds are formed. The coating 30 deposited by the methodaccording to the invention has a high electrical conductivity and formsa high diffusion barrier. It has an essentially crystalline property anda layer thickness of approximately 0.65 nm to 650 nm.

The preceding discussion serves to illustrate the inventions covered bythe patent application as a whole, each also independently improvingupon the prior art at least through the following combinations offeatures, wherein two, more or all of these combinations of features mayalso be combined further, namely:

A method for ALD coating of a substrate 17 with a layer containing Ti,Si, N, wherein a reaction gas is fed into a process chamber 10containing the substrate 17 in a plurality of successive steps 1, 2, 3in one or more n, m, k, l, p, q, r cycles and then a flushing gas is fedinto the same process chamber,

-   -   wherein TiN is deposited in a first step 1 with a reaction gas        containing TI and with a reaction gas containing N,    -   in a second step 2 which follows the former step, TiSi is        deposited with a reaction gas containing Ti and a reaction gas        containing Si,    -   and in a third step 3 following the second step 2, TiSiN is        deposited with a reaction gas containing Ti, with a reaction gas        containing N and with a reaction gas containing Si is deposited.

A method which is characterized in that a cycle consisting ofintroducing the reaction gas containing Ti, flushing the process chamber10 with an inert gas, feeding the reaction gas containing N and flushingthe process chamber 10 with a reaction gas is carried n times in thefirst step 1, where n>1.

A method which is characterized in that in the second step 2 a firstsubstep 2.1 consisting of introducing the reaction gas containing Ti andthen flushing the process chamber 10 with an inert gas is carried out mtimes, where m>1 and in which a second substep 2.2 in which the reactiongas containing Si is introduced into the process chamber 10 and then theprocess chamber 10 is flushed with the inert gas, is carried out k timeswhere k>1.

A method which is characterized in that the two substeps 2.1,2.2 arecarried out 1 times in succession where 1>1.

A method which is characterized in that in the third step 3 a firstsubstep 3.1, in which the reaction gas containing Ti is introduced intothe process chamber 10 and then the process chamber 10 is flushed withan inert gas, next the reaction gas containing N is introduced into theprocess chamber 10 and then the process chamber 10 is flushed with aninert gas is carried out p times where p>1, and in a second substep 3.2the process gas containing Si is fed into the process chamber 10 andnext the process chamber 10 is flushed with an inert gas wherein thesecond substep 3.2 is carried out q times in succession, where q>1.

A method which is characterized in that the third step 3 is carried outr times in succession where r>1.

A method which is characterized in that the reaction gas containing Tiis introduced at a partial pressure of less than 12×10⁻³ millibar; thereaction gas containing Si and having a partial pressure between 1×10⁻³and 4×10⁻³ millibar is introduced and/or the reaction gas containing Nis introduced at a partial pressure between 9×10⁻³ and 8×10⁻¹ millibar.

A method that is characterized in that the total pressure inside theprocess chamber 10 is in the range between 0.6 and 6 millibar and thesteps 1, 2, 3 are carried out at temperatures in the range between 400and 700° C., wherein the times for feeding the reaction gases are in therange between 0.4 and 60 seconds.

A method which is characterized in that the reaction gas containing Tiis TiCl₄, TDMAT or TDEAT and/or the reaction gas containing Si isSiH₂Cl₂, SiHCl₃, SiCl₄, SiH₄ or Si₂H₆ and/or the reaction gas containingN is NH₃ or MMH.

A coating which is characterized in that the nitrogen content in thefirst and second boundary ranges 31, 32 is greater than that in the coreregion 33.

A coating which is characterized in that the core region 33 isessentially free of nitrogen.

A coating which is characterized in that the surface 34 of the secondboundary region facing away from the substrate 17 is free of nitrogen.

All the features disclosed here are essential to the invention (eitheralone or in combination with one another). Thus, the full disclosurecontent of the respective/attached priority documents (photocopy of theprevious patent application) has also been included for the purpose ofincorporating features of these documents into the claims in the presentpatent application). The dependent claims characterized with theirfeatures independent inventive refinements of the prior art even withoutthe features of a claim that has been included by way of reference, inparticular to compile divisional applications on the basis of theseclaims. The invention defined in each claim may additionally have one ormore of the features defined in the preceding description, in particularfeatures provided with reference numerals and/or cited in the list ofreference numerals. The invention also relates to design forms in whichindividual features of those cited in the preceding description are notimplemented, in particular inasmuch as they are recognizably notessential for the respective intended purpose or can be replaced byother means having the same technical effect.

List of Reference Numerals 1 Process step 2 Process step 2.1 Substep 2.2Substep 3 Process step 3.1 Substep 3.2 Substep 4 Transport step 5Heating step 6 Transport step 10 Process chamber 11 Reactor housing 12Gas inlet element 13 Gas outlet opening 14 Gas outlet 15 Heater 16Susceptor 17 Substrate 18 Chamber 19 Chamber 20 Chamber 21 Chamber 22Mass flow controller 23 Mass flow controller 24 Mass flow controller 25Mass flow controller 30 Coating 31 Boundary region 32 Boundary region 33Core region 34 Surface D Axis of rotation k Cycle number l Cycle numberm Cycle number n Cycle number p Cycle number q Cycle number r Cyclenumber

1. A method for forming a contact structure of a semiconductor devicethe method comprising: providing in a reaction chamber a substratecomprising an exposed silicon surface; forming a conductive diffusionbarrier on the exposed silicon surface by cyclic thermal deposition,forming the conductive diffusion barrier comprising: forming anitrogen-free high conductivity region by alternatingly exposing thesubstrate to a first titanium-containing precursor and a firstsilicon-containing precursor; and forming a nitrogen-containing highdiffusion barrier region on the high conductivity region byalternatingly exposing the substrate to a second titanium-containingprecursor, a nitrogen-containing precursor and a secondsilicon-containing precursor.
 2. The method of claim 1, wherein theexposed silicon surface is a polysilicon surface.
 3. The method of claim2, wherein forming the high conductivity region comprises forming atitanium silicide (TiSi₂) layer.
 4. The method of claim 3, whereinforming the high diffusion barrier region comprises forming a titaniumsilicon nitride (TiSiN) layer.
 5. The method of claim 4, wherein formingthe TiSiN layer comprises directly contacting the TiSi₂ layer with theTiSiN without an intervening layer.
 6. The method of claim 5, whereinforming the TiSiN layer comprises forming a plurality of TiN sublayersalternating with a plurality of Si sublayers.
 7. The method of claim 6,wherein forming the TiSiN layer comprises forming the TiN sublayers andthe Si sublayers that are intermixed to form a homogeneous layer.
 8. Themethod of claim 6, wherein forming the TiSiN layer comprises forming theTiN sublayers and the Si sublayers that remain as discrete andalternating layers.
 9. The method of claim 8, wherein forming the TiSiNlayer comprises forming a first one of the TiN sublayers to contact theTiSi₂ layer.
 10. The method of claim 8, wherein forming the TiSiN layercomprises terminating with a Si layer that is free of nitrogen.
 11. Themethod of claim 10, further comprising forming a metallic layer on theSi layer to form the contact structure.
 12. The method of claim 4,further comprising forming a TiN layer interposed between thepolysilicon surface and the TiSi₂ layer.
 13. A method for forming acontact structure of a semiconductor device, the method comprising:forming a nitrogen-free high conductivity region on a silicon surface byalternatingly exposing the substrate to a first titanium-containingprecursor and a first silicon-containing precursor; and forming anitrogen-containing high diffusion barrier region on the highconductivity region, forming the high diffusion barrier regioncomprising: alternatingly exposing the substrate to a secondtitanium-containing precursor and a nitrogen-containing precursor toform a TiN sublayer, and exposing the substrate to a secondsilicon-containing precursor to form a Si sublayer.
 14. The method ofclaim 13, wherein the silicon surface is a polysilicon surface.
 15. Themethod of claim 13, wherein forming the high conductivity region forms atitanium silicide (TiSi₂) layer.
 16. The method of claim 13, whereinforming the high diffusion barrier region comprises forming a pluralityof TiN sublayers alternating with a plurality of Si sublayers to form atitanium silicon nitride (TiSiN) layer.
 17. The method of claim 16,wherein forming the TiSiN layer comprises forming a homogeneous TiSiN.18. The method claim
 17. wherein forming the TiSiN layer comprisesforming a plurality of discrete TiN sublayers alternating with aplurality of discrete Si sublayers.
 19. The method of claim 18, whereinthe TiSiN layer terminates with a Si layer that is free of nitrogen. 20.The method of claim 19, further comprising forming a metallic layer onthe Si layer to form the contact structure.